Structure and mechanical properties for binary blends of polypropylene and ethylene-1-hexene copolymer

Abstract

The structure and mechanical properties of the injection-molded products for the binary blends composed of an isotactic polypropylene (PP) and a rubbery ethylene-1-hexene copolymer (EHR) were studied. The following two types of blends were employed: one is the incompatible blend of PP and ethylene-rich EHR; the other is the compatible blend of PP and 1-hexene-rich EHR. The incompatible blend shows a phase-separated morphology, in which EHR domains in the skin layer highly orient to the flow direction. On the other hand, the compatible blend shows fairly homogeneous morphology in the skin and core regions, in which EHR molecules are dissolved into the amorphous PP region. The measurements of birefringence and infrared dichroism revealed that the magnitude of molecular orientation along the flow direction for the compatible blend is larger than that for the incompatible blend. Nevertheless, it was also found that anisotropy of the mechanical properties for the compatible blend is less prominent, which is attributed to lack of the mechanical connection between neighbor crystalline fragments aligned perpendicular to the flow direction. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 701–713, 1999